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How are floods predicted?

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Welcome to CoreFacts, where we're always short on time and big on science. I'm Jessica Robertson. Today's question is about floods.

How are floods predicted?

First I want to point out that floods are a dangerous hazard throughout the world. On average in the United States, about 165 people are killed and about $2 billion of damage occurs each year. Most people underestimate the power of flood waters.

Several types of data can be collected to assist hydrologists predict when and where floods might occur. The first is monitoring the amount of rainfall occurring on a realtime basis. Second, monitoring the rate of change in river stage on a realtime basis can help indicate the severity and immediacy of the threat. Third, knowledge about the type of storm producing the moisture, such as duration, intensity and areal extent, is valuable for determining possible severity of the flooding. And fourth, knowledge about the characteristics of a river's drainage basin, such as soil-moisture conditions, ground temperature, snowpack, topography, vegetation cover and impermeable land area, can help to predict how extensive and damaging a flood might become.

The National Weather Service collects and interprets rainfall data throughout the United States and issues flood watches and warnings as appropriate. The USGS maintains a network of streamflow-gaging stations throughout the country and produces flood estimation maps. More information on floods and real-time flood monitoring is available at and from the Hydrologic Information Center at

And now you know. Join us again every weekday for a new CoreFact. For other CoreFacts, or for CoreCast, our in-depth science podcast, go to If you'd like to have a question featured on our show, give us an email at or a phone call at 703-648-5600. Remember, long distance fees do apply.

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